Iron-Catalyzed Reductive Carboxylation of Arenes with CO 2 via Thianthrenium Salts

C–C bond formation catalyzed by abundant and nontoxic iron has attracted increasing attention. Although much progress has been made, iron-catalyzed reductive coupling is still limited. In this work, the reductive carboxylation of aryl thianthrenium salts with CO 2 catalyzed by iron is developed. This protocol is characterized by mild conditions and excellent functional group tolerance. Due to the nontoxicity of iron, this method can be applied for the late-stage C–H carboxylation of complex drug molecules to provide multiple carboxyl drugs. Preliminary mechanistic studies reveal that an Fe(0)–Fe(I)–Fe(II)–Fe(0) catalytic cycle may be involved in this reaction. This reaction expands the types of iron-catalyzed reactions, which may promote the application of iron catalysis in organic synthesis.